Certain embodiments of the present invention relate to materials and processes for manufacturing components such as cutting tools.
The synthesis and processing of nanophase or nanostructured materials, i.e. materials with grain sizes less than about 100 nm, is currently of great interest because these materials are believed to have properties different from and often superior to the properties of conventional bulk materials. One application for nanostructured materials is in the cutting tool industry, where properties such as hardness and fracture toughness are important for producing wear resistant cutting tools. However, problems relating to both the synthesis of nanostructured powders and the consolidation of the nanostructured powders exist.
Nanostructured materials have been produced using synthesis methods such as electrodeposition, melt spun, spray conversion, high pressure sputtering, chemical vapor deposition and sol-gel processing. Cemented carbide powders having particles including nanosized grains have been formed using a spray conversion techniques such as those described in U.S. Pat. Nos. 5,230,729, 5,352,269 and 5,651,808. These patents describe for formation of powders in the tungsten carbide-cobalt system (WCxe2x80x94Co). WCxe2x80x94Co powders are often used for cutting tool applications. Controlled, high rate synthesis of nanometer sized powders having particles that are uniform in morphology and composition has been difficult to achieve. Powders tend to include particles on the order of micrometers in size, which are made up of agglomerates of nanosized grains.
Production of bulk nanostructured components having a high density and a nanostructured grain size has proven difficult due to the competing mechanisms of densification and grain growth. Consolidation of cemented carbide (WCxe2x80x94CO) powders into dense structures is typically carried out at elevated temperatures using liquid phase sintering, which utilizes temperatures above the eutectic temperature of the material. The high temperatures during liquid phase sintering, however, lead to undesirable grain growth. For example, a powder starting with 50 nm WC grains prior to liquid phase sintering may end up with WC grains larger than 1 xcexcm after liquid phase sintering. Grain growth inhibitors such as VC and Cr3C2 may be added to the composition in an effort to control the grain growth during densification. The grain growth inhibitors, however, may deleteriously affect the physical properties of the material.
One embodiment of the present invention relates to a consolidated cemented carbide body having a mean carbide grain size of less than 100 nm. The body is consolidated to at least 98% of its theoretical density. The body has an average hardness in the range of 2000 to 2400 HV and an average fracture toughness of at least 16 MPa mxc2xd.
Another embodiment relates to a consolidated nanostructured component including a microstructure with at least 25 percent of the grains being no greater than 100 nm in diameter and the component being at least 98 percent of its theoretical density.
Another embodiment relates to a method for fabricating a nanograined component from a nanograined powder composition, including forming a compact from the nanograined powder composition. Sufficient heat is applied to the compact to generate at least one exothermic reaction while the compact is at a temperature lower than its eutectic temperature. Pressure is applied to the powder compact during the heating operation to consolidate the powder compact. The application of heat and pressure are controlled to inhibit grain growth and form a component a nanograined microstructure that is at least 98 percent dense at a temperature lower than the eutectic temperature.
Yet another embodiment relates to a method for forming a body of at least 99.9% density, including providing a powder composition that exhibits an exothermic behavior in the solid state, the powder composition having a eutectic temperature. An amount of the powder composition is shaped into a body. Increasing amounts of heat and pressure are applied to the body to form a microstructure that is at least 99.9% dense, and the application of heat and pressure to the body is stopped at a temperature above the exotherm temperature and below the eutectic temperature of the composition.
Still another embodiment relates to a method for consolidating a nanograined powder including providing an electrically conductive nanograined powder mass. A high voltage electric current is applied to the powder mass and pressure is applied to the powder mass to consolidate the mass.